|
چکیده
|
The microstructure of the bonding area consisted of several distinct zones based on the bonding parameters. At temperature of 1050 °C, the isothermal solidification was completed after 60 min, while at 1100 °C it was completed after 30 min. The only γ-Ni solid solution was observed in the solidified zone. Samples with incomplete isothermal solidification showed a continuous eutectic structure in the centerline of the solidified zone. This eutectic structure produced due to the solidification of the remaining melt and consisted of three phases i. e. Ni3B, Cr2B, and γ-Ni solid solution. Two diffusion affected zones were seen on both sides of the solidification zone. These zones consisted of secondary phases such as (Fe,Cr)2B and boron carbon nitride. By increasing the time and temperature, the microhardness profile became more uniform owing to the removal of these eutectic structures. The maximum shear strength belonged to the bonded specimen at 1100 °C for 45 min, which is due to the fully isothermal solidification, the removal of brittle eutectic phases and more uniform microstructure of the bonding zone. The reason for increasing the shear strength with increasing temperature was the reinforcement of the bonding zone by the solution hardening owing to the inter-diffusion of the alloying elements.
|